Channel adding/dropping filters in high quality optical networks form a key functional element in dense wavelength-division multiplexed (DWDM) optical fiber networks. They are used to either separate (slice) or multiplex (interleave) signals that are on equally spaced apart channels (wavelengths). For example, a typical 1×2 coupler is connected such that a single input port receives a DWDM signal and two output ports provide the sliced DWDM signal into odd and evenly spaced channels respectively for further slicing and/or processing. Such a coupler may also have its connections reversed so as to perform a multiplexing operation. Unfortunately, such devices do not have a constant gain transfer function in the passbands when functioning as a slicer. That is, as the individual wavelengths are separated from the incoming signal, they lose signal quality because the optimal rectangular response desired in such device is not realized. One attempt to improve this condition is to pass the incoming DWDM signal through multiple stages of Mach-Zhender devices to achieve a flatter and more rectangular response. This approach is not always effective because of the inherently varied manufacturing tolerances of each devices and is generally inopposite to the concept of having integrated optical techniques for signal processing.